As known, stirrers having a complete enamel coating with separable paddles are employed in completely closed (coverless) reaction vessels, provided with manholes of reduced diameter so that they can withstand elevated working pressures.
They can be employed, in particular in case one wants to exchange in the closed coverless vessel a previously used stirrer of small dimensions, e.g. a propeller type stirrer for a larger stirrer, i.e. an anchor type stirrer.
The detachable paddle system has the advantage that the paddles can be exchanged on an installed shaft, leaving the whole mechanical apparatus unchanged.
Essentially two types of enamel coated stirrers with separable paddles with direct gasket-free paddle to shaft connection are presently known. They are as follows:
1) the type described in the Sybron, U.S. Pat. No. 4,221,488, in which the connection between shaft and paddle hub is obtained by a cryogenic system on perfectly cylindrical contact surfaces machined in such a way as to have a slight dimensional interference between the inserting and the receiving member (at a same temperature); and
2) the type described in the De Dietrich, European Patent No. 145,370, in which the end of the shaft has an incorporated paddle bearing hub provided with radial cavities for the insertion of the single paddles having an insertion stem, the connection between hub and paddle taking place on slightly conical surfaces and is performed by forced insertion.